In this type of device, the location of the motive power source which causes the opening and closing valve to open and close has been a source of problems, and has in particular made it difficult to downsize the engine. Moreover, since the opening and closing valve and the motive power source are located at positions remote from each other, and since the direction of their movements is not uniform, when they are connected by link mechanisms or cable type arrangements, their drive side and driven side shaft ends project from the crank case, the cylinder, the exhaust line and the like, and as a result, some sort of covering is required to protect the exposed parts against stones or mud, and to provide oil seals and the like.